1. Field of the Invention
The present invention relates to apparatus for use in the oil industry, and, more particularly, to a float collar apparatus for use in oil well drilling operations.
2. Description of the Prior Art
Float collars are utilized by the oil well industry with respect to operations for running in and cementing casing liners down a wellbore. An example of a prior art float collar is the Multi-Purpose Float Collar manufactured and sold by Davis-Lynch, Inc. The Multi-Purpose Float Collar comprises a tubular housing having a bore therethrough and two spring-activated flapper valves which are held in an open position by a sliding sleeve installed in the bore of the float collar. Once the sleeve is forced out of the bore of the float collar, the spring-activated flapper valves are free to rotate to their closed positions.
In practice, a float collar, such as the Multi-Purpose Float Collar of Davis-Lynch, Inc., is installed within the lower end of a casing liner prior to running the casing liner down a wellbore. When the spring-activated flapper valves of the float collar are held in an open position by the sliding sleeve, a clear passage is provided through the casing liner. This open position permits drilling fluid to flow freely through the float collar as the casing liner is being run downhole, which helps to reduce surge pressure against the borehole walls and permits the casing liner to be more readily lowered to total depth. Additionally, if a tight hole condition is encountered during running in of the casing liner, drilling fluid can be pumped downward through the casing liner to circulate drilling fluid around the tight hole condition thereby freeing the casing liner.
Once the casing liner is lowered to total depth, the sliding sleeve of the float collar is actuated using a drop ball, which seats in a ball seat which is coupled to the sliding sleeve. The sliding sleeve is held in place by shear pins installed in the lower portion of the sleeve. Pressure is then increased above the drop ball until the shear pins shear, at which time the sleeve is displaced axially out of the float collar. This movement of the sleeve frees the spring-activated flapper valves to rotate to a closed position. In the closed position, the flow path through the casing liner is obstructed such that any fluid passing through the casing liner must overcome the resistance of the spring-activated flapper valves to establish communication between the lower end of the casing liner and the annulus between the casing liner and the borehole.
During cementing operations, cement is pumped downward through the casing liner at sufficiently high pressure to overcome the resistance of the spring-activated flapper valves. Once cement pumping operations cease, the spring-activated flapper valves close and seal the passage through the casing liner. This prevents the cement from flowing back upward into the casing liner. This effect is also known in the art as xe2x80x9cback-flowxe2x80x9d or xe2x80x9cu-tubexe2x80x9d action. Finally, once cementing operations are completed, the entire float collar assembly is drilled out of the casing liner to reestablish an unobstructed flow path through the wellbore.
While prior art float collars have produced desirable results for the oil well industry, an undesirable feature of prior art float collars is that once cementing operations are complete, prior art float collars require approximately six hours to drill out of the casing liner to reestablish the unobstructed flow path. This relatively long drill out time is due in large part to the high metal content of components of the float collar. Prior art float collars are fabricated almost entirely of metals, e.g. aluminum. While the use of such metals allows the float collar assembly to be set at pressures up to 3000 psi, the metal components of the float collar assembly become a disadvantage when cementing operations are completed and valuable time and resources must be expended during drilling out the float collar.
Accordingly, it would be desirable to have a float collar which can be drilled out in substantially less time than prior art float collars. This novel and useful result has been achieved by the present invention.
Apparatus in accordance with the present invention comprises a float collar assembly for regulating the passage of fluid through a tubular member, such as a casing liner. The float collar assembly is positioned within the tubular member cased in cement at the lower end of the tubular member.
In a first embodiment of the present invention, a float collar assembly comprises an outer housing having an axial bore therethrough and one or more spring-activated flapper valves arranged within the housing. The spring-activated flapper valves are activated by an internal valve-actuating sleeve which is fabricated from a hardened plastic material. Such hardened plastic material may include a modified nylon blend material, such as cast type 6 nylon having enhanced thermal-resistant, weather-resistant, and bearing properties, or a nylon-phenolic laminate. The actuating sleeve is initially held inside the housing by a connecting means. While the actuating sleeve is connected to the housing, the spring-activated flapper valves are secured by the actuating sleeve in an open position. A drop ball seat is integral with the actuating sleeve and is located at the bottom of the actuating sleeve. The seat receives a drop ball thereby creating a seal which blocks fluid flow through the tubular member. Subsequently, fluid pressure is increased above the drop ball seat to activate the connecting means to release the actuating sleeve and displace the actuating sleeve downward from the housing. Once the actuating sleeve is displaced from the housing, the spring-activated flapper valves are free to rotate to a closed position. In the closed position, the spring-activated flapper valves obstruct passage through the tubular member.
In another embodiment of the present invention, the connecting means is a set of shear pins which connect the actuating sleeve to the housing. When the connecting means is activated by the drop ball, the set of shear pins is sheared. Once the set of shear pins is sheared, the actuating sleeve is free to displace axially downward out of the housing.
In still another embodiment of the present invention, the connecting means is a shoulder formed on the upper end of the actuating sleeve which protrudes radially outward and a groove formed in the axial bore of the housing. Initially, the shoulder of the actuating sleeve engages the groove of the housing to connect the actuating sleeve to the housing. When the connecting means is activated, the shoulder of the actuating sleeve is sheared by the groove of the housing. Once the shoulder is sheared, the actuating sleeve is free to displace axially downward out of the housing.
In yet another embodiment of the present invention, the connecting means is a lightweight metal shearing sleeve attached to the upper end of the actuating sleeve having a shoulder formed on the upper end of the shearing sleeve which protrudes radially outward and a groove formed in the axial bore of the housing. The shoulder of the shearing sleeve engages the groove of the housing to connect the actuating sleeve to the housing. The connecting means also includes a recess formed between the upper end and lower end of the shearing sleeve such that thickness of the wall of the shearing sleeve is smallest at the recess. When the connecting means is activated, the shearing sleeve is sheared at the recess at a predetermined pressure. Once the shearing sleeve is sheared, the actuating sleeve is free to displace axially downward out of the housing.
Furthermore, while components of prior art float collars are fabricated almost entirely from metal, the float collar apparatus of the present invention is fabricated from a combination of metal and non-metal components, or from non-metal components only. This resultant float collar assembly provides a savings in time and resources expended during drilling out of the float collar.